The Church teaches that the mercy and justice of God emphasizes that they are not contradictory, but rather exist in perfect harmony within God. It affirms that God is just, meaning He upholds the moral order of creation. This involves giving each person their due, both in terms of rewards for good and consequences for sin. It requires that sin, which disrupts the relationship between God and humanity, has consequences. This is reflected in the concept of divine judgment.
On the other hand, God’s mercy is His infinite love and compassion, — His desire to forgive and heal the wounds of sin. It is the manifestation of His overwhelming love for humanity.
The Church teaches that God’s mercy is most fully revealed in Jesus Christ, whose sacrifice on the cross offers forgiveness and redemption to all who repent and believe. It is taught that Gods mercy is greater than his justice. Gods desire is that all people be saved, and enter into heaven.
“Justice and mercy, justice and charity on which the Church’s charity is hinged, are two different realities only for the human person. For we distinguish carefully between a just act and an act of love. For us “just” means “what is due to the other”, while “merciful” is what is given out of kindness. One seems to exclude the other. Yet for God it is not like this: justice and charity coincide in him; there is no just action that is not also an act of mercy and pardon, and at the same time, there is no merciful action that is not perfectly just.” – Pope Benedict XVI
When we reflect on mercy the question naturally arises about the relationship of mercy to justice. God is not merciful at the expense of his justice. Mercy does not exclude His justice, nor is it opposed to it (MV §21). How could it? “God’s justice is his mercy given to everyone [oppressed by slavery to sin and its consequences] as a grace that flows from the death and resurrection of Jesus Christ” (MV §21).
God’s justice entails His taking sin seriously, indeed, “of all the injustice we have committed before God” (NG, 58), by virtue of taking away and atoning for our guilt in history. In the reality of the atoning work of Jesus Christ where there is a turning from real wrath to real grace. Pope Francis explains, “Thus the Cross of Christ is God’s judgment on all of us and on the whole world” (MV §21).
Here Pope Francis echoes St. John Paul II who teaches that God has shown us his justice and mercy “in the cross of Christ, on which the Son, consubstantial with the Father, renders full justice to God.” His death on the cross, he adds, “is also a radical revelation of mercy, or rather of the love that goes against what constitutes the very root of evil in the history of man: against sin and death” (Dives in Misericordia [DM], §8, emphasis added).
References
https://www.ewtn.com/catholicism/library/justice-and-mercy-in-the-logic-of-god-6914